1. Field of the Invention
The present invention relates to a liquid crystal display device and a controlling method thereof, and more particularly, to a liquid crystal display device and a controlling method thereof that have an active control of brightness.
2. Discussion of the Related Art
In general, a liquid crystal display device controls light transmissivity of liquid crystal cells in accordance with image data to display pictures. In particular, a transmissive type liquid crystal display device includes a back light unit on a rear surface of a liquid crystal display panel to irradiate light on the liquid crystal display panel.
FIG. 1 is a schematic configuration of a transmissive type liquid crystal display device according to the related art. In FIG. 1, the liquid crystal display device includes a back light unit 12 on a rear surface of a liquid crystal display panel 11. The liquid crystal display panel 11 includes a liquid crystal layer (not shown). In addition, the liquid crystal panel 11 receives video data, RGB, and adjusts a light transmittance of the liquid crystal layer based on the video data, thereby controlling a transmission of light irradiated from the back light unit 12 to display an image.
The back light unit 12 includes a light guide plate (not shown) for converting light from a line light source into surface light, and a diffusion sheet and an optical sheet (not shown) for improving uniformity and efficiency of the light. The line light source includes a lamp having a discharge tube for generating white light in accordance with a tube current received from an inverter 14. The inverter 14 converts DC power from a power supply 13 into AC power and boosts the AC power, to thereby generate the tube current.
However, a brightness of the back light unit 12 is fixed. Thus, the liquid crystal display device according to the related art has a lower display brightness in comparison with a cathode ray tube (CRT) display device. Further, the liquid crystal display device according to the related art has a fixed maximum brightness and a low contrast ratio, such that display quality deteriorates.